Not quite so fantastic, then, when a few days later we saw another one, this time without the comfort of a guide, because it was in our room. I didn't scream, but only because I was struck mute with terror. This one had no orange knees, was instead velvety black all over, and was in a strategic position in command of the door. We were trapped, awaiting a knight in shining armour. According to our rescuer later, it was a pica- caballos, a "horse-stinger", so called because it produces enough venom to kill a horse.
But this is what you should expect when you go to Costa Rica. It is, after all, famed for its wildlife. With 35,000 species of insects, the odds are that one day one of them will make it into your bed, especially if you stay in a cabin set in lush gardens, or even a shelter within one of the numerous national parks.
Lest you be put off by such fears, I should quickly stress that the countryside is beautiful and well protected , the beaches largely deserted, especially in the rainy season, and the people very friendly. And in addition to the creepy-crawlies, there are 200 species of mammals and 850 species of birds.
It's enough to make you a bird-watcher. Hummingbirds of a myriad colours sip nectar while you have breakfast outside, the forest teems with parrots and macaws, the rivers are home to herons of every hue and beautiful white egrets.
In Tortuguero national park, an unaccompanied walk almost turned into a sprint at the sound of something large and hoarse roaring, until we remembered that this is the unlikely cry of the howler monkey. Howlers are common here, along with spider monkeys and white-faced capuchins, whole families of them putting on a bravura performance of acrobatics once they had an audience. The sighting of a scarlet macaw - a pair, in fact - was completely unexpected, as they are becoming rare due to deforestation and poaching. But identification was easy, because of the size - they reach up to 17 inches fully grown - and its fabulous primary colours.
Tortuguero is a remote area of coastal rainforest in north-east Costa Rica, accessible only by boat. Even by sea it was once difficult to reach from the southeastern Caribbean coast, because of the treacherous waters. If the currents didn't get you, the sharks would. Now there is an inland waterway to connect the tiny community here to the rest of the world. It is steamy: the average humidity is 70 per cent, with 400 inches of rain a year. But if this makes it inhospitable to man, it is very welcoming to one mammal - the turtle, which nests here.
Green turtles, leatherbacks, loggerheads and hawksbills all lay their eggs here at different times of year, and tagging surveys of the green turtle since 1955 have shown that even though they spend the rest of their cycle feeding off the coast of Panama and Colombia to the south, and Nicaragua, Honduras, some even as far away as Florida to the north, many still return here to lay.
From Tortuguero you can take a canoe up one of the many tributaries, which is a good way to see wildlife, as very little is disturbed by the presence of a canoe. On the five-hour journey, our captain, Enrico, spotted birds and beasts; us amateurs had to be almost upon them before we would see them. Despite us eagerly examining every floating log we passed for signs of crocodile behaviour, it was Enrico who saw him first - a big, mean-looking croc (what other kind is there?) who obliged us with a good view for a few moments, before diving down to emerge who knows where? We didn't wait to find out.
Enrico also saw the sloth, well camouflaged by its colouring and by the speed, or rather lack of it, of its movements. A three-toed sloth (and believe me its toe-nails, being about four inches long, are one of its distinguishing features) has no predators here, which is just as well since it moves at less than a mile a year. Up in the hilly forests around Monteverde, sloths are taken by harpy eagles. On the way up river we saw a shy male, discernible by orange-yellow marking on his back (is this so the females can tell the difference, I wondered?), and returning next day downriver we encountered a female, completely unperturbed when we settled the boat right under her tree and seemingly just as curious about us as we were about her.
In sharp contrast to Tortuguero is Monteverde, an area of cloud forest high up in the Tilaran mountain range to the north of the capital, San Jose. Getting here is something of an adventure, along a dirt and stone track with more holes than a wedge of Gouda. Here, too, we had a guide for one morning, to lead us to the hidden creatures of the forest. As we entered the reserve, we spied two timid raccoons, peering inquisitively from lush vegetation a safe distance away, but we were greeted by a contingent of coatis, not in the least shy, which look like a very cute cross between a badger and an anteater. At least, they played cute until a banana appeared, whereupon they declared war on the raccoons.
Monteverde Cloud Forest Reserve is a private, project, originally begun by American Quakers in 1951 - and still expanding. As its name implies, it takes its moisture from the clouds which often envelop it, rather than being drenched as rainforests are - it gets half the rainfall of Tortuguero. The thick vegetation therefore differs, and because of an elevation of close on a mile, which makes it much cooler than the rainforest, the species that live there are different, too.
Our guide, Adrian, had a great repertoire of birdsong (supplemented by skilful use of a tape recorder) and excelled at finding us elusive birds, even luring down a family of quails that had at first scarpered away. We heard the rusty-gate bird, better known as the black-faced solitary, and he pointed out a slate-throated redstart and an olive-striped flycatcher. He engaged us with tales of his father's near demise at the fangs of a coral snake, which is supposed to kill you within two hours. As we left, a rare tayra - a kind of forest-dwelling otter - scampered across the road as if in farewell.